Beaufort Sea coast erosion, shoreline evolution, and sediment flux

Understanding shoreline evolution, and in particular, the consequences of shoreline erosion is a major societal concern that threatens to become even more important in the future with the impacts of climate change. Thus, it is necessary to improve both knowledge of the dominant physical processes controlling medium to long-term shoreline evolution and the capabilities of morphological evolution models to simulate beach changes at these spatial and temporal scales. Empirical models may be an ideal choice for modelling complex and dynamic environments such as sandy beaches at large spatial (beach) and long temporal (years to decades) scales. They reproduce the effects of the main morphodynamical processes with low computational cost and relatively high accuracy, in particular when high quality, long-term data are available for calibration. Here, to broaden its range of application, a cross-shore equilibrium model, which has demon- strated its accuracy and efficiency in reproducing shoreline and intertidal beach profile changes at several micro and macrotidal beaches, is extended to couple it with a longshore beach evolution modelling approach. The selection of a particular longshore model (based on a one-line approach), and its implementation and validation with benchmark test cases of shoreline evolution caused by the effects of diffusion, high angle wave instabilities, and coastal structures are presented. The new hybrid model is applied at Narrabeen beach to reproduce the long-term evolution of beach contours near the shoreline. The model is calibrated and tested using the 40-year timeseries of monthly subaerial beach profile surveys conducted along 5 cross-shore profiles along the 3.6km-long Narrabeen-Collaroy embayment. The novelty of the current work is to focus on reproducing changes at different altitudes, with the objective of assessing the cross-shore variability of the longshore sediment flux, which is assumed constant in most one-line longshore transport models. The coupled model performance is discussed, and the results are compared to existing studies that have simulated shoreline evolution at Narrabeen using other morphological change models.

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A 14 - 0 ka record of trends and events of sea ice cover, primary production and freshwater discharge in the Beaufort Sea, Arctic Ocean

10.5194/egusphere-egu2020-4699 ◽

2020 ◽

Author(s):

Junjie Wu ◽

Ruediger Stein ◽

Kirsten Fahl ◽

Nicole Syring ◽

Jens Hefter ◽

...

Keyword(s):

Sea Ice ◽

Primary Production ◽

Beaufort Sea ◽

Ice Cover ◽

Sediment Flux ◽

The Arctic ◽

Proxy Records ◽

Ice Retreat ◽

Sea Ice Retreat ◽

Natural Climate

The Arctic is changing rapidly, and one of the main and most obvious features is the drastic sea-ice retreat over the past few decades. Over such time scales, observations are deficient and not long enough for deciphering the processes controlling this accelerated sea-ice retreat. Thus, high-resolution, longer-term proxy records are needed for reconstruction of natural climate variability. In this context, we applied a biomarker approach on the well-dated sediment core ARA04C/37 recovered in the southern Beaufort Sea directly off the Mackenzie River, an area that is characterized by strong seasonal variability in sea-ice cover, primary productivity and terrigenous (riverine) input. Based on our biomarker records, the Beaufort Sea region was nearly ice-free in summer during the late Deglacial to early Holocene (14 to 8 ka). During the mid-late Holocene (8 to 0 ka), a seasonal sea-ice cover developed, coinciding with a drop in both terrigenous sediment flux and primary production. Supported by multiple proxy records, two major flood events characterized by prominent maxima in sediment flux occurred near 13 and 11 ka. The former is coincident with the Younger Dryas Cooling Event probably triggered by a &#160;freshwater outburst from the Lake Agassiz. The origin of the second (younger) one might represent a second Mackenzie flood event, coinciding with meltwater pulse IB/post-glacial flooding of the shelf and related increased coastal erosion. Here, our interpretation remains a little bit speculative, and further research is needed and also in progress.

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